1. Field of the Invention
The present invention relates to supply circuits of the type including a rectifier and a storage capacitor, for supplying a load via a regulation circuit such as a switched-mode circuit.
2. Discussion of the Related Art
At the present time, many devices electrically supplied from the mains include a switched-mode power supply. The power is extracted from the network in the form of current peaks of short duration. These current peaks disturb the network efficiency. The effects of these current peaks worsen with the number of devices connected to the network and incorporating a switched-mode power supply. Accordingly, electric distribution companies have imposed several standards to improve the power factor of power supplies.
FIG. 1 shows a conventional diagram of provision of a d.c. power supply from the mains. Terminals X and Y of the a.c. supply are connected to input terminals of a rectifying bridge 1, output terminals A and B of which are connected to a storage capacitor C1 and to a load L. It will be assumed that load L incorporates a regulation circuit, for example, a switched-mode power supply, connected to a load. Further, a resistor r of low value for limiting the current surges of the system upon power-on is often to be found in series with capacitor C1.
FIG. 2A shows, as a function of time, rectified mains voltage V.sub.XY and voltage V.sub.A B, between terminals A and B (neglecting the effect of resistor r). It is assumed that at a time t0, the voltage across capacitor C1 is higher than the mains voltage. Then, the voltage between terminals A and B corresponds to the voltage across capacitor C1 which progressively discharges into load L. From a time t1, the rectified mains voltage becomes higher than the voltage across the capacitor, and the mains ensures the supply of load L and the recharge of capacitor C1. From a time t2, the voltage on the capacitor becomes higher than the mains voltage and, again, the capacitor supplies the load. This is repeated at the next halfwave (times t3 and t4).
FIG. 2B shows the shape of the current extracted from the mains between times t1-t2 and t3-t4. Theoretically, the current has a substantially triangular shape. In practice and as illustrated in FIG. 2B, the current is substantially sinusoidal due to the mains impedances and, more specifically, it corresponds to a sine wave peak, that is, its shape is substantially parabolic. The current peaks are symmetrical with respect to their maximum and this maximum can be relatively high.